A motor-driven vehicle, e.g. a motor-driven wheelchair, includes two drive wheels which are mounted on a vehicle body on its opposite sides and are driven by electric motors coupled to them. The motors drive the respective drive wheels with driving forces determined according to manual-driving-forces exerted by a person who drives the wheelchair which are detected by manual-driving-force sensing units mounted on the wheelchair.
For example, Japanese Unexamined Patent Publication (KOKAI) No. HEI 7-75219 (of which content is disclosed in U.S. patent application Ser. No. 08/798,804, which is a division of U.S. patent application Ser. No. 08/477,039 filed on Jun. 7, 1995 and now abandoned) discloses a motor-driven wheelchair which includes two manual-driving-force sensing units mounted on the wheelchair body for each of motors providing assisting force. Manual driving forces exerted to the respective manual-driving-force sensing units drive the associated drive wheels. At the same time, the respective manual-driving-force sensing units detect the magnitudes of the manual-driving-forces applied to them, and the motors drive the associated drive wheels with force determined according to the detected manual driving forces. According to the invention disclosed in this Japanese unexamined patent publication, the two drive wheels are independently controlled.
Since manual driving forces are exerted to the vehicle body by a human, e.g. an attendant to the person who is on the wheelchair, or the person on the wheelchair himself, the times at which the manual driving forces are applied to the respective manual-driving-force sensing units may differ, or, sometimes, the magnitudes of the manual driving forces applied to the respective manual-driving-force sensing units may differ because of difference in muscular strength between his right and left arms. In the motor-driven wheelchair disclosed in the above-cited Japanese unexamined publication, the two drive wheels are independently controlled by their associated motors in relation to the manual driving forces as detected by the manual-driving-force sensing units for the respective drive wheels. Accordingly, difference in timing of application of manual driving forces or difference in magnitude of manual driving forces as described above may cause motor forces to be applied to the respective drive wheels at different times, or may cause different magnitudes of motor force to be applied to the drive wheels. Therefore, it is difficult to drive the wheelchair straight.
In order to drive the wheelchair straight, the attendant or the person on the wheelchair must endeavor to properly control the timing of application of manual driving forces or the magnitudes of the manual driving forces. Then it is more or less difficult to drive such wheelchair in a desired manner.
Accordingly, an object of the present invention is to provide a motor-driven vehicle which can be driven straight despite difference in timing of application or difference in magnitude of manual driving forces, and which is easy to drive.
A motor-driven vehicle need be also driven to rotate clockwise or counterclockwise. The fact that the vehicle can be driven straight despite difference in timing of application or in magnitude of manual driving forces may pose a problem when the vehicle should be rotated.
Accordingly, another object of the present invention is to provide a motor-driven vehicle which can be driven straight despite difference in timing of application or in magnitude of manual driving forces, and which is easy to drive, and which also can be easily rotated clockwise or counterclockwise when necessary.